Field of the Invention
The present invention relates to a holographic image display device, and more particularly, to a holographic image display device and a method for driving the same which may stabilize luminance of a holographic image and reduce flicker.
Discussion of the Related Art
Stereoscopic image display devices displaying 3D images with enhanced realism have been applied to various fields, such as medicine, education, gaming, movies, and TV industries. As methods for displaying stereoscopic images, there are stereoscopy, holography, integral imaging, etc. Among these methods, the holography method is an auto-stereoscopic method in which an observer may view a stereoscopic image equal to an actual object using a hologram, and is known as the most ideal method in which an observer may feel a stereoscopic image having an excellent 3D effect without fatigue.
The holography method uses a principle of recording an interference signal acquired through superposition of light reflected by an object (an object wave) and light having coherence (a reference wave) and reproducing the interference signal. Recordation of an interference pattern, formed by joining an object wave, which is formed by scattering of laser light having high coherence through collision with an object, with a reference wave incident in a different direction, on a film is referred to as a hologram. When the object wave and the reference wave are joined, the interference pattern is formed by interference therebetween, and amplitude and phase information of the object are recorded in such an interference pattern. Restoration of the stereoscopic image, recorded as the hologram, into a 3D image by emitting reference light to the interference pattern is referred to as holography.
In a holographic image display device, a computer system generates a holographic interference pattern image corresponding to a stereoscope image and transmits the holographic interference pattern image to a spatial light modulator (SLM), laser light (reference light) emitted from a laser backlight unit is converted into surface light by a surface light converter, and the surface light is emitted to the SLM. The SLM including a transmission type liquid crystal display panel displays a holographic interference pattern and diffracts the emitted light, thus projecting a holographic image at a viewing point.
However, since liquid crystal response time of the liquid crystal display panel used in the SLM is slow, if the laser backlight unit is continuously turned on, light reaches the viewing point even while the liquid crystals are driven and thus, an imperfect image may be generated. In order to prevent such a problem, a blinking technique in which the laser backlight unit is turned off while the liquid crystals are driven each frame (while image data of one frame is applied to the panel) and is then turned on after the liquid crystals have been completely driven (after image data of one frame has been completely applied to the panel) is used. Since the laser backlight unit is turned on only at a point of time when the liquid crystals have been completely driven, such a blinking technique may eliminate an imperfect image and display only a perfect image of one frame. Therefore, the blinking technique is applied for the purpose of relieving eye fatigue and allowing an observer to watch a comfortable image.
However, since the laser backlight unit reaches a saturation state in which each laser light is stabilized only if a designated time has been elapsed after the laser backlight unit has been converted from the off state to the on state, the blinking technique unstably varies luminance of a holographic image.
FIG. 1 is a graph representing luminance variation of specific laser light according to time. From FIG. 1, it may be understood that the laser light is saturated after a designated time from turning-on of a laser backlight unit has been elapsed.
However, since the blinking technique performs time division in which each frame is divided into an off period and an on period, the on period is shorter than a period for which laser light reaches a saturation state and thus, laser light having unstable luminance is used. Thereby, when an observer views a holographic image, eye fatigue of the observer may be caused and a clear image may not be acquired.